Segment sensitive scheduling

ABSTRACT

Systems and methods of scheduling sub-carriers in an OFDMA system in which a scheduler takes into account channel conditions experienced by the communication devices to optimize channel conditions. The scheduler can partition a set of sub-carriers spanning an operating bandwidth into a plurality of segments. The segments can include a plurality of global segments that each includes a distinct non-contiguous subset of the sub-carriers spanning substantially the entire operating bandwidth. One or more of the global segments can be further partitioned into a plurality of local segments that each has a bandwidth that is less than a channel coherence bandwidth. The scheduler determines channel characteristics experienced by each communication device via reporting or channel estimation, and allocates one or more segments to communication links for each device according to the channel characteristics.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present application for patent is a divisional of patent applicationSer. No. 11/260,924 entitled “CHANNEL SENSITIVE SCHEDULING” filed Oct.27, 2005, pending, and assigned to the assignee hereof and herebyexpressly incorporated by reference herein, and claims priority toProvisional Application No. 60/710,461 entitled “CHANNEL SENSITIVESCHEDULING” filed Aug. 22, 2005.

The present application for patent is related to the followingco-pending U.S. patent applications:

“Shared Signaling Channel” by having Attorney Docket No. 060058, filedconcurrently herewith, assigned to the assignee hereof, and expresslyincorporated by reference herein; and

“Mobile Wireless Access System” having Attorney Docket No. 060081, filedconcurrently herewith, assigned to the assignee hereof, and expresslyincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Disclosure

The disclosure relates to the field of wireless communications. Moreparticularly, the disclosure relates to scheduling of resources in awireless communication system.

2. Description of Related Art

Communication devices operating in wireless communication systems can beaffected by drastic changes in the channel conditions experienced bycommunication device. The channel conditions can be affected byextraneous interferers and can be affected by changes in the physicalrelationship and terrain separating a wireless transmitter from areceiver.

It is known that a wireless signal originating at the transmitter isattenuated by the physical distance to the receiver. Additionally, it isknown that multipath signals from the transmitter to the receiver canresult in fading of the channel.

A wireless communication system can compensate for attenuation byincreasing transmit power or by increasing modulation or coding gainassociated with the transmit signal. A wireless communication system maypartially compensate for multipath fading by implementing a broadbandsignal that allows the receiver to separately identify multipathsignals.

A wireless communication system implementing frequency divisionmultiplexing can operate over a relatively wide frequency band. Theoperating band may be sufficiently wide that distinct communicationdevices operating at the same location but at different operatingfrequencies may experience substantially different channel conditionsand channel fading. Additionally, each communication device may notoperate with a sufficiently broad band signal to allow the device tocompensate for multipath fades.

It is desirable to have the ability to communicate in a frequencydivision multiplex communication system with multiple communicationdevices in a manner that compensates for, or otherwise substantiallyeliminates the effects of frequency selective channel conditions.

BRIEF SUMMARY OF THE INVENTION

Systems and methods of scheduling sub-carriers in an OFDMA system aredisclosed, in which a scheduler takes into account channel conditionsexperienced by the communication devices to optimize channel conditions.The scheduler can partition a set of sub-carriers spanning an operatingbandwidth into a plurality of segments. The segments can include aplurality of global segments that each includes a distinctnon-contiguous subset of the sub-carriers spanning substantially theentire operating bandwidth. One or more of the global segments can befurther partitioned into a plurality of local segments that each has abandwidth that is less than a channel, carrier, or coherence bandwidth.The scheduler determines channel characteristics experienced by eachcommunication device via reporting or channel estimation, and allocatesone or more segments to communication links for each device according tothe segment characteristics.

The disclosure includes a method of segment sensitive scheduling in anOrthogonal Frequency Division Multiple Access (OFDMA) communicationsystem including a plurality of sub-carriers spanning an operatingfrequency band. The method includes partitioning the operating frequencyband into a plurality of segments, determining a segment preferenceindicative of a preferred segment based upon channel characteristicsexperienced by a receiver, and assigning a subset of sub-carriers withinthe preferred segment to a particular communication link associated withthe segment preference.

The disclosure includes a method of segment sensitive scheduling thatincludes partitioning the operating frequency band into a plurality ofsegments, determining user data constraints, assigning sub-carriers froma global segment having a non-contiguous subset of sub-carriers spanninga substantial fraction of the operating band if the user dataconstraints include a data bandwidth requirement greater than a coherentbandwidth of a carrier, segment, or the like determining, if the databandwidth requirement is not greater than the coherent bandwidth of acarrier, segment or the like, a segment preference indicative of apreferred local segment based upon channel characteristics experiencedby a receiver, the preferred local segment selected from a plurality oflocal segments, each of the plurality of local segments having abandwidth less than the coherent bandwidth, and assigning a subset ofsub-carriers within the preferred local segment to a communication linkassociated with the segment preference.

The disclosure includes an apparatus for segment sensitive scheduling.The apparatus includes a receiver module configured to receive a pilotsignal, a channel estimator coupled to the receiver and configured todetermine a channel estimate corresponding to each of a plurality ofsegments spanning the operating frequency band based on the pilotsignal, each of the segments having a bandwidth less than a coherentbandwidth, a signal mapper configured to map serial data symbols to asubset of the plurality of sub-carriers in the OFDMA communicationsystem, and a resource scheduler coupled to the channel estimator andconfigured to determine a first preferred segment based on the channelestimates, select the subset of the plurality of sub-carriers fromwithin the first preferred segment, and further configured to controlthe signal mapper to map the data symbols to the subset of the pluralityof sub-carriers.

The disclosure includes an apparatus for segment sensitive schedulingthat includes a receiver module configured to receive a reverse linkpilot signal and at least one channel characteristic reporting message,and a scheduler coupled to the receiver module and configured todetermine, based on the reverse link pilot signal, a channelcharacteristic corresponding to each of a plurality of segments spanningthe operating frequency band, each of the segments having a bandwidthless than a coherent bandwidth, the scheduler configured to determine areverse link assignment based on the channel characteristics and furtherconfigured to determine a forward link resource assignment based on theat least one channel characteristic reporting message.

The disclosure includes an apparatus for segment sensitive schedulingthat includes means for determining a segment preference indicative of apreferred segment from a plurality of segments substantially spanningthe operating band based upon channel characteristics experienced by areceiver, and means for assigning a subset of sub-carriers within thepreferred segment to a particular communication link associated with thesegment preference.

The disclosure includes a method of reporting segment characteristics.The method includes receiving a pilot signal, determining a segmentcharacteristic corresponding to each of a plurality of segments spanningthe operating band, each segment having a bandwidth less than a coherentbandwidth, determining a preferred segment from the plurality ofsegments, comparing the channel characteristic corresponding to thepreferred segment to a reporting threshold, and generating a reportingmessage based on the preferred segment if the channel characteristiccorresponding to the preferred segment exceeds the reporting threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of embodiments of the disclosurewill become more apparent from the detailed description set forth belowwhen taken in conjunction with the drawings, in which like elements bearlike reference numerals.

FIG. 1 is a simplified functional block diagram of an embodiment of acommunication system having segment sensitive scheduling.

FIG. 2 is a simplified functional block diagram of an embodiment of atransmitter with segment sensitive scheduling.

FIG. 3 is a simplified functional block diagram of an embodiment of areceiver in a system implementing segment sensitive scheduling.

FIG. 4 is a simplified flowchart of an embodiment of a method of segmentsensitive scheduling.

FIG. 5 is a simplified flowchart of an embodiment of a method of segmentcharacteristic reporting in a system implementing segment sensitivescheduling.

DETAILED DESCRIPTION OF THE INVENTION

Segment sensitive scheduling of sub-carrier resources in an OrthogonalFrequency Division Multiple Access (OFDMA) communication system providesfor a form of multi-user frequency diversity. A segment sensitivescheduler operates to schedule communication links with communicationdevices on available sub-carriers in the OFDMA system having maximumgain.

Frequency selectivity is a common characteristic of broadband wirelesscommunication systems. Users with the same average channel strength mayhave quite different channel strength at particular frequency tones. Theinterference a user observes is in general also frequency selective.Hence, it would be desirable for users to communicate over the frequencytones with high signal level or low interference level depending on userdata requirements and information resources of the system. The segmentsensitive scheduling schemes discussed herein implement schedulingfrequency tones, such as sub-carriers in an OFDMA system, based on theuser frequency or channel characteristics under overhead and latencyconstraints.

One set of beneficiaries of segment sensitive scheduling include userswith low signal to noise ratio (SNR), limited assignment size and lowmobility. According to information theory, SNR improvement translatesinto capacity gain through a logarithmic function, hence, the capacitygain is larger if the SNR is low. In practical systems, the capacity ofhigh SNR users may also be limited by the capacity of the highest ordermodulation and coding scheme that saturates at certain SNR, whichdiminishes the improvements due to further improvement in SNR. High datarate users require transmission of signals over a large fraction of thetotal bandwidth, which reduces the potential gain of scheduledtransmission over average segment SNR. The scheduling and transmissiondelay can make it difficult to schedule high mobility users on theirpreferred tones based on past channel observations. Fortunately, manyusers in a wide area network satisfy the SNR, assignment size, andmobility requirements to benefit from segment sensitive scheduling.

A scheduler in an OFDMA system can be configured to schedule forwardlink communications from a base station to a user terminal, reverse linkcommunications from a user terminal to a base station, or a combinationof forward link and reverse link communications. A scheduler can performforward link scheduling independent of reverse link scheduling. In otherembodiments, the scheduler can relate forward link scheduling to reverselink scheduling.

The scheduler operates to schedule channel resources based, at least inpart, on channel characteristics experienced by the communicationdevices. In one embodiment, the scheduler can determine the channelcharacteristics based on one or more channel quality indicator (CQI)included in one or more reporting messages communicated from acommunication device to the scheduler. In another embodiment, thescheduler can be configured to determine the channel characteristicsthrough channel estimation. In another embodiment, the scheduler candetermine the channel characteristics using a combination of reportingmessages and channel estimation.

FIG. 1 is a simplified functional block diagram of an embodiment of awireless communication system 100 configured to schedule resources basedon channel characteristics. The system 100 includes one or more fixedelements that can be in communication with a user terminal 110. Althoughthe description of the system 100 of FIG. 1 generally describes awireless telephone system or a wireless data communication system, thesystem 100 is not limited to implementation as a wireless telephonesystem or a wireless data communication system nor is the system 100limited to having the particular elements shown in FIG. 1.

The user terminal 110 can be, for example, a wireless telephoneconfigured to operate according to one or more communication standards.The user terminal 110 can be a portable unit, a mobile unit, or, astationary unit. The user terminal 110 may also be referred to as amobile unit, a mobile terminal, a mobile station, user equipment, aportable, a phone, and the like. Although only a single user terminal110 is shown in FIG. 1, it is understood that a typical wirelesscommunication system 100 has the ability to communicate with multipleuser terminals 110.

The user terminal 110 typically communicates with one or more basestations 120 a or 120 b, here depicted as sectored cellular towers.Other embodiments of the system 100 may include access points in placeof the base stations 120 a and 120 b. In such a system 100 embodiment,the BSC 130 and MSC 140 may be omitted and may be replaced with one ormore switches, hubs, or routers.

As used herein, a base station may be a fixed station used forcommunicating with the terminals and may also be referred to as, andinclude some or all the functionality of, an access point, a Node B, orsome other terminology. An access terminal may also be referred to as,and include some or all the functionality of, a user equipment (UE), awireless communication device, terminal, a mobile station or some otherterminology.

The user terminal 110 will typically communicate with the base station,for example 120 b, that provides the strongest signal strength at areceiver within the user terminal 110. Each of the base stations 120 aand 120 b can include a scheduler configured to assign and schedule thesegment resources. The one or more base stations 120 a-120 b can beconfigured to schedule the channel resources used in the forward link,reverse link, or both links.

Each of the base stations 120 a and 120 b can be coupled to a BaseStation Controller (BSC) 140 that routes the communication signals toand from the appropriate base stations 120 a and 120 b. The BSC 140 iscoupled to a Mobile Switching Center (MSC) 150 that can be configured tooperate as an interface between the user terminal 110 and a PublicSwitched Telephone Network (PSTN) 150. In another embodiment, the system100 can implement a Packet Data Serving Node (PDSN) in place or inaddition to the PSTN 150. The PDSN can operate to interface a packetswitched network, such as network 160, with the wireless portion of thesystem 100.

The MSC 150 can also be configured to operate as an interface betweenthe user terminal 110 and a network 160. The network 160 can be, forexample, a Local Area Network (LAN) or a Wide Area Network (WAN). In oneembodiment, the network 160 includes the Internet. Therefore, the MSC150 is coupled to the PSTN 150 and network 160. The MSC 150 can also beconfigured to coordinate inter-system handoffs with other communicationsystems (not shown).

The wireless communication system 100 can be configured as an OFDMAsystem with communications in both the forward link and reverse linkutilizing OFDM communications. The term forward link refers to thecommunication link from the base stations 120 a or 120 b to the userterminal 110, and the term reverse link refers to the communication linkfrom the user terminal 110 to the base stations 120 a or 120 b. Both thebase stations 120 a and 120 b and the user terminal 110 may allocateresources for channel and interference estimation. For example, both thebase stations 120 a and 120 b and the user terminal 110 may broadcastpilot signals that are used be the corresponding receivers for channeland interference estimation.

The wireless communication system 100 can include a set of sub-carriersthat span an operating bandwidth of the OFDMA system. Typically, thesub-carriers are equally spaced. The wireless communication system 100may allocate one or more sub-carriers as guard bands, and the system 100may not utilize the sub-carriers within the guard bands forcommunications with the user terminal 110.

In one embodiment, the wireless communication system 100 can include2048 sub-carriers spanning an operating frequency band of 20 MHz. Aguard band having a bandwidth substantially equal to the bandwidthoccupied by six sub-carriers can be allocated on each end of theoperating band. Therefore, in this embodiment, over 2000 sub-carriersare available for allocation to communications with the user terminal110.

The wireless communication system 100 can be configured to partition theoperating band into a plurality of operating segments, each of which caninclude at least one sub-carrier. The wireless communication system 100can partition the forward link and reverse links to be identical.Alternatively, the forward link and reverse link segment definitions canbe distinct.

The segments can each have a distinct set of sub-carriers, such that nosub-carrier is allocated to more than one segment. In anotherembodiment, segments may have overlapping sub-carrier assignments. Thesegments can be contiguous frequency bands within the operating band orcan be non-contiguous bands within the operating band. In oneembodiment, each segment can span at least 16 sub-carriers or a multipleof 16 sub-carriers, although not all of the sub-carriers may beallocated to the same segment. Additionally, the segments may not beequally sized, and segments nearer the edge of the operating band may besmaller than segments closer to the center of the operating band.

In one embodiment, the wireless communication system 100 can beconfigure to partition a plurality of global segments, where each globalsegment has a bandwidth that spans a substantial fraction of the totaloperating band. Each of the global segments typically includes anon-contiguous subset of the total set of sub-carriers. In oneembodiment, two global segments may be defined, with odd sub-carriersallocated to a first global segment and even sub-carriers allocated to asecond global segment. In another embodiment, three global segments canbe defined, with each global segment assigned every third sub-carrier inthe operating band. Of course, the global segments do not need to haveequally spaced sub-carriers, and do not need to span substantially theentire operating band. For example, two global segments can be definedthat span one-half of the operating band, with sub-carriers in the halfof the operating band alternately assigned to the global segments.Various other segment partitions may be defined, and the disclosure isnot limited to any particular segment partition.

The wireless communication system 100 can also be configured topartition the operating band into one or more local segments. In oneembodiment, each of the local segments can include a contiguous subsetof all of the sub-carriers in the operating band. In another embodiment,at least one local segment can include a non-contiguous subset ofsub-carriers. In one embodiment, each of the sub-carriers in the localsegment can be within a coherent bandwidth of any other sub-carrierassigned to the same local segment. The coherent bandwidth correspondsto the bandwidth in which no substantial frequency selective fadingoccurs relative to another frequency within the band. For example, anembodiment can partition the operating band into multiple segments eachhaving a bandwidth of approximately 1.25 MHz.

For example, the International Telecommunication Union (ITU) defines achannel model designated the Ped-B channel. This channel model has acoherent bandwidth on the order of hundreds of kilohertz. Thus, a localsegment can have a bandwidth that is less than the coherent bandwidth ofthe Ped-B channel model. With such a local segment constraint, theresource assignments within any particular local segment are relativelyfrequency non-selective. That is, a channel estimate within one localsegment can be valid for any combination of sub-carriers within thelocal segment. For example, a wireless communication system 100 with anoperating bandwidth of 20 MHz can partition the band into local segmentsof approximately 1.25 MHz each.

In one embodiment, the operating band can be partitioned into apredetermined number of local segments, each having substantially equalnumber of contiguous sub-carriers. In another embodiment, the wirelesscommunication system 100 can include both global and local segments. Forexample, the wireless communication system 100 can define two globalsegments, with sub-carriers alternately assigned to each of the globalsegments. The wireless communication system 100 can select one of theglobal segments and can further partition the selected global segmentinto a plurality of local segments.

The wireless communication system 100 can include one more schedulersthat are configured to allocate sub-carrier resource assignments to thevarious communication links within the system. For example, the wirelesscommunication system 100 can include one or more schedulers at each ofthe base stations 120 a and 120 b. In one embodiment, each of the basestations 120 a and 120 b can include a first scheduler configured toschedule forward link sub-carrier assignments within the coverage areaand a second scheduler configured to schedule reverse link sub-carrierassignments within the coverage area. Because each individual userterminal 110 typically has no knowledge regarding the sub-carrierassignments of other user terminals 110 within a particular coveragearea, it may be advantageous for the wireless communication system 100to implement a centralized reverse link scheduler for each coverage arealocated at the base stations 120 a and 120 b.

The scheduler can be configured to determine a resource assignment,including sub-carriers and corresponding segments, based in part on thechannel characteristics experienced by the communication device. Forexample, the forward link scheduler can be configured to assignsub-carriers and segments based on the channel characteristicsexperienced by the base station, for example 120 a, when communicatingwith a particular user terminal 110. Similarly, the reverse linkscheduler can be configured to adding sub-carriers and segments to eachuser terminal 10 based in part on the channel characteristicsexperienced by the reverse link signal.

The schedulers can determine the channel characteristics on the forwardand reverse links based on channel analysis, channel characteristicreporting, or a combination of channel analysis and reporting. Theschedulers can be configured to assign the sub-carriers and segments toa communication link that exhibit the greatest signal level or that havethe lowest interference. The scheduler can determine the number ofsub-carriers assigned to a particular communication link based on avariety of factors, including the bandwidth of the signal communicated.The scheduler can also take into account other scheduling criteria, suchas fairness, signal latency constraints, and other criteria, whenassigning segments and sub-carriers to a communication link.

The wireless communication system 100 can maintain some level ofinterference diversity between the various communication channels byimplementing frequency hopping. A communication link, such as a forwardlink signal transmitted by a base station 120 a or 120 b, or a reverselink signal transmitted by a user terminal 110, can be configured tofrequency hop across a plurality of sub-carriers based on an initialsub-carrier assignment and a predetermined frequency hopping algorithm.The wireless communication system 100 can implement a frequency hoppingalgorithm that enforces frequency hopping within the assigned segments.Therefore, a forward link signal that is assigned a subset of carrierswithin a segment will perform frequency hopping within the segment inorder to provide some level of interference diversity.

The wireless communication system 100 can be configured to FrequencyDivision Duplex (FDD) the forward and reverse links. In a FDDembodiment, the forward link is frequency offset from the reverse link.Therefore, forward link sub-carriers are frequency offset from thereverse link sub-carriers. Typically, the frequency offset is fixed,such that the forward link channels are separated from the reverse linksub-carriers by a predetermined frequency offset. The forward link andreverse link may communicate simultaneously, or concurrently, using FDD.In an FDD system, channel estimates determined for the forward orreverse link signals are typically not accurate channel estimates forthe complementary FDD reverse or forward link channels. Thus in FDDsystems, channel characteristic reporting may be used to communicatechannel characteristics to the appropriate scheduler.

In another embodiment, the wireless communication system 100 can beconfigured to Time Division Duplex (TDD) the forward and reverse links.In such an embodiment, the forward link and reverse links can share thesame sub-carriers, and the wireless communication system 100 canalternate between forward and reverse link communications overpredetermined time intervals. In TDD, the allocated frequency channelsare identical between the forward and reverse links, but the timesallocated to the forward and reverse links are distinct. A channelestimate performed on a forward or reverse link channel is typicallyaccurate for the complementary reverse or forward link channel becauseof reciprocity.

The base stations, 120 a and 120 b, and the user terminal 110 can beconfigured to broadcast a pilot signal for purposes of channel andinterference estimation. The pilot signal can include broadband pilotssuch as a plurality of CDMA waveforms or a collection of narrow bandpilots that span the overall spectrum. The broadband pilots could alsobe a collection of narrow band pilots staggered in time and frequency.

In one embodiment, the pilot signal can include a number of tonesselected from the OFDM frequency set. For example, the pilot signal canbe formed from uniformly spaced tones selected from the OFDM frequencyset. The uniformly spaced configuration may be referred to as astaggered pilot signal.

The scheduler in the base station, 120 a or 120 b, can determine thechannel characteristics in each of the segments based on the pilotsignals. The recipient of the pilot signal, for example the userterminal 110 in the forward link direction, can determine an estimate ofthe channel and interference based on the received pilot signal.Additionally, the user terminal 110 can determine an estimate of thesignal quality of the received signal, such as by determining a receivedsignal to noise ratio (SNR). The signal quality of the received signalcan be quantified as a channel quality indicator (CQI) value, which canbe determined, in part based on the estimated channel and interference.In a wireless communication system 100 implementing multiple operatingsegments, the user terminal 110 can determine a channel and interferenceestimate corresponding to each of the operating segments and determineone or more CQI values based on the various channel and interferenceestimates.

The user terminal 110 can report a CQI value back to the base station,for example 120 a, and a scheduler in the base station 120 a can comparethe CQI value for each of the operating segments to determine thesegment(s) to allocate to the user terminal 110. The user terminal 110can report the CQI directly in a reporting message or can generate areporting message that includes data and information derived from theCQI value. For example, the user terminal 110 can be configured todetermine the segment having the greatest CQI value and report the CQIvalue and identity of the corresponding segment. As will be discussed ingreater detail below, the user terminal 110 can be configured to reportthe CQI value or related reporting message regularly, on an assignedbasis, or on a probabilistically determined basis.

The wireless communication system 100 can implement a retransmissionprocess, such as a Hybrid Automatic Repeat Request (HARQ) algorithm. Insuch a system, a transmitter may send an initial transmission at a firstdata rate and may send a subsequent retransmissions due to unsuccessfulreceipt at lower rates. HARQ incremental redundancy retransmissionschemes can improve system performance in terms of providing earlytermination gain and robustness. However, improvements attributable tosegment sensitive scheduling can be reduced if the scheduledtransmission is based on out-dated information, which may occur in HARQsystems. If the segments and sub-carriers are not reallocated forretransmissions of an HARQ protocol, the segment which has high SNR atthe time of the first transmission may get faded and results in a lossin performance.

Thus, in one embodiment, the wireless communication system 100 can beconfigured to re-determine the channel characteristics and canre-schedule sub-carrier and segments assigned to a particularcommunication link for HARQ retransmissions. Alternatively, theprobability of channel fade occurring in the duration of the longestretransmission duration of a HARQ protocol, and the probability of aHARQ re-transmission occurring during channel fade may be sufficientlylow. In such a situation, the wireless communication system may notreschedule sub-carriers and segments for HARQ retransmissions and mayallow the communication link to experience a slight degradation if achannel fade should occur during the HARQ retransmissions.

FIG. 2 is a simplified functional block diagram of an embodiment of anOFDMA transmitter 200 such as can be incorporated within a base stationof the wireless communication system of FIG. 1. The following discussiondescribes an embodiment in which the transmitter 200 is implemented in abase station of a wireless communication system configured for OFDMAcommunications. The transmitter 200 is configured to transmit one ormore OFDMA signals to one or more user terminals. The transmitter 200includes a data buffer 210 configured to store data destined for one ormore receivers. The data buffer 210 can be configured, for example, tohold the data destined for each of the user terminals in a coverage areasupported by the corresponding base station.

The data can be, for example, raw unencoded data or encoded data.Typically, the data stored in the data buffer 210 is unencoded, and iscoupled to an encoder 212 where it is encoded according to a desiredencoding rate. The encoder 212 can include encoding for error detectionand Forward Error Correction (FEC). The data in the data buffer 210 canbe encoded according to one or more encoding algorithms. Each of theencoding algorithms and resultant coding rates can be associated with aparticular data format of a multiple format Hybrid Automatic RepeatRequest (HARQ) system. The encoding can include, but is not limited to,convolutional coding, block coding, interleaving, direct sequencespreading, cyclic redundancy coding, and the like, or some other coding.

A wireless communication system implementing a HARQ algorithm can beconfigured to retransmit prior data that was not successfully decoded.The HARQ algorithm can be configured to provide a maximum number orretransmissions, and each of the retransmissions can occur at a lowerrate. In other embodiments, the HARQ algorithm can be configured totransmit some of the retransmissions at the same rate.

The encoded data to be transmitted is coupled to a serial to parallelconverter and signal mapper 214 that is configured to convert a serialdata stream from the encoder 212 to a plurality of data streams inparallel. The scheduler 230 determines the number of sub-carriers, theidentity of the sub-carriers, and the corresponding frequency segmentsfor each user terminal. The scheduler 230 provides the resourceallocation information to the signal mapper 214. The number of carriersallocated to any particular user terminal may be a subset of allavailable carriers. Therefore, the signal mapper 214 maps data destinedfor a particular user terminal to those parallel data streamscorresponding to the data carriers allocated to that user terminal bythe scheduler 230.

The output of the serial to parallel converter/signal mapper 214 iscoupled to a pilot module 220 that is configured to allocate apredetermined portion of the sub-carriers to a pilot signal. In oneembodiment, the pilot signal can include a plurality of equally spacedsub-carriers spanning substantially the entire operating band. The pilotmodule 220 can be configured to modulate each of the carriers of theOFDMA system with a corresponding data or pilot signal.

The output of the pilot module 220 is coupled to an Inverse Fast FourierTransform (IFFT) module 222. The IFFT module 222 is configured totransform the OFDMA carriers to corresponding time domain symbols. Ofcourse, a Fast Fourier Transform (FFT) implementation is not arequirement, and a Discrete Fourier Transform (DFT) or some other typeof transform can be used to generate the time domain symbols. The outputof the IFFT module 222 is coupled to a parallel to serial converter 224that is configured to convert the parallel time domain symbols to aserial stream.

The serial OFDMA symbol stream is coupled from the parallel to serialconverter 224 to a transceiver 240. In the embodiment shown in FIG. 2,the transceiver 240 is a base station transceiver configured to transmitthe forward link signals and receive reverse link signals.

The transceiver 240 includes a forward link transmitter module 244 thatis configured to convert the serial symbol stream to an analog signal atan appropriate frequency for broadcast to user terminals via an antenna246. The transceiver 240 can also include a reverse link receiver module242 that is coupled to the antenna 246 and is configured to receive thesignals transmitted by one or more remote user terminals.

The scheduler 230 can be configured to receive reverse link signals,including the reverse link pilot signals and channel characteristicreporting messages, and determine the segments and sub-carriers toassign to the communication links for each of the user terminals. Asdescribed earlier, the scheduler 230 can use the reverse link pilotsignals to determine the reverse link resource allocation. Additionally,the scheduler 230 can use the reverse link pilot signals to determineforward link resource allocation for TDD systems in which OFDMA systemuses the same bandwidth for the forward and reverse links. In theembodiment shown in FIG. 2, the scheduler 230 can be used to scheduleboth forward and reverse link resources. In other embodiments, aseparate scheduler can be used for the forward and reverse links.

The reverse link receiver module 242 can couple the reverse pilotsignals to a channel estimator 232, shown in this embodiment as part ofthe scheduler 230. Of course, the channel estimator 232 is not limitedto implementation within the scheduler 230 and may be implemented insome other module, such as the reverse link receiver 242. The channelestimator 232 can determine, for each of the user terminals broadcastinga reverse pilot signal, which segment has the highest signal power orhighest Signal to Noise Ratio (SNR). Additionally, the channel estimator232 can determine which of the segments has the lowest interferencelevel.

High bandwidth communication links that are assigned to the globalsegments may not experience a significant improvement when thesub-carrier assignments over a resource allocation scheme that allocatesresources based on highest average channel strength. Thus, in oneembodiment, the channel estimator 232 determines the channelcharacteristics for each local segment and does not determine thechannel characteristics for the global segments. Alternatively, thechannel estimator 232 can be configured to determine an average channelstrength for the global segments.

The channel estimator 232 can communicate the channel characteristicinformation to the resource scheduler 234 that operates to schedule thesub-carriers to the appropriate forward links based on the channelcharacteristic information. The resource scheduler 234 can also includereverse link scheduling messages on one or more overhead channels in theOFDMA system.

In one embodiment, the wireless communication system can implement anassignment algorithm that minimizes the overhead associated withresource assignments. The assignment method can be referred to as“sticky assignment.” The assignment algorithm may alternatively bereferred to as persistent assignment or enduring assignment. In stickyassignment a user's assignment does not expire unless an explicitde-assignment message is received. An assignment message to other usersthat include a user's current resource ID is considered as ade-assignment message of the corresponding resource of this user. A useris assigned certain segment corresponding to a particular frequency bandbased upon favorable channel characteristics. This user will keepreceiving or sending information over sub-carriers within the segmentuntil a new assignment is received. Given limited scheduling overhead ofN simultaneous messages, the system can potentially simultaneouslyschedule M users, where M is much greater than N.

Once resources are allocated to a particular communication link, thecommunication link can continue with that assignment. However, thesub-carrier assignments are not necessarily static. For example, theresource scheduler 234 can implement a channel tree that is a logicalmap of the available resources. The resources scheduler 234 can beconfigured to assign resources based on the logical structure of thechannel tree. The resource scheduler 234 or some other module, such asthe frequency hopping module 238, can map the logical resourceassignment from the channel tree to a physical assignment thatcorresponds to physical sub-carriers of the OFDM system.

The channel tree can be organized in a branch structure with multiplebranches. The branches eventually terminate in a lowest level of thetree, referred to as a leaf node or a base node. Every branch node inthe channel tree can be assigned an identifying node index.Additionally, each leaf node or base node can be assigned a node index.Typically, the number of leaf nodes can correspond to the number ofphysical sub-carriers available in the OFDM system.

Every node includes a corresponding node index, and higher level branchnodes can be used to identify all of the nodes underneath the branchnode in the channel tree. Thus, assigning a particular branch node to aparticular communication link assigns all of the leaf nodes appearingunderneath the particular branch node to that communication link.

Although each node of the channel tree, including each leaf node or basenode, can be arbitrarily mapped to any physical resource, it may beadvantageous to provide some mapping constraints on the channel tree.For example, the leaf nodes can be divided into groups, where each groupof leaf nodes corresponds approximately to the number of sub-carrierswithin a segment. Thus, some of the leaf nodes can be divided into agroup that corresponds to a global segment, while other leaf nodes canbe divided into a group that corresponds to a local segment.

The branch nodes can thus be organized according to the grouping of theleaf nodes, and assigning a branch node corresponds to assigning all ofthe resources in nodes appearing underneath the branch node. It may beadvantageous to have two distinct channel trees, one corresponding toresources assigned to global segments and another channel treecorresponding to the resources assigned to local segments.

If the resource scheduler 234 assigns a branch node sufficiently deep inthe channel tree to a particular communication link based on the channelcharacteristics, the channel tree can be constrained such that all ofthe lower nodes underneath the branch node will be assigned to the samesegment. This channel tree organization can simplify the mapping of thelogical nodes to the physical resources.

The resource scheduler 234 or the frequency hopping module 238 can mapthe logical channel tree assignments to physical sub-carrierassignments. Therefore, the logical node assignments can remain stablewhile the physical sub-carriers mapped to the nodes can vary.

A frequency hopping module 238 can be configured to improve interferencediversity by implementing frequency hopping within the assigned segment.The frequency hopper module 238 can, for example, implement apseudorandom frequency hopping scheme for each assigned sub-carrier. Thereceiver can be configured to utilize the same frequency hoppingalgorithm to determine which sub-carriers are assigned to itscorresponding link. For example, the frequency hopping module 238 canimplement a frequency hopping algorithm that results in the same logicalnodes being mapped to different physical sub-carriers at differentinstances.

The scheduler 230 can include a CQI receiver 236 configured to receiveand process channel characteristic reporting messages generated by theuser terminals and transmitted on the reverse link. Such reportingmessages may be used to schedule the forward link assignments in FDDsystems, or systems in which the reverse pilots do not sufficientlyrepresent the forward link resources.

The manner and information included in the reporting messages aredescribed in further detail below in relation to the description of thereceiver embodiment. For the purposes of resource assignment, it issufficient to describe the reporting messages as including some measureof channel characteristics, channel quality, segment preference, or someother indication that can be related to a segment preference.

The CQI receiver 236 is configured to receive the reporting messages anddetermine, based at least in part on the reporting messages, if thepresent resource allocation should be sustained or if the sub-carrier orsegment allocations should be modified. The CQI receiver 236 cancommunicate the assignment information to the resource scheduler 234that is configured to control the signal mapper 214 to implement thesub-carrier and segment assignments. The resource scheduler 234 can alsoreport any new sub-carrier or segment assignments to the correspondingreceiver. For example, the resource scheduler 234 can be configured togenerate a control message that is communicated to the appropriatereceiver using an overhead channel.

FIG. 3 is a simplified functional block diagram of an embodiment of areceiver 300. The receiver 300 can be, for example, part of a userterminal 110 shown in FIG. 1. The following discussion describes areceiver 300 implemented within a user terminal of an OFDMA wirelesscommunication system using reporting messages for the determination ofthe forward link assignments.

The receiver 300 can include an antenna 356 coupled to a transceiver 350configured to communicate over a wireless channel with the transmitter200 shown in FIG. 2. The transceiver 350 can include a forward linkreceiver module 352 configured to receive the forward link wirelesssignals, via the antenna 356, and generate a serial baseband symbolstream.

The output of the receiver module 352 of the transceiver 350 is coupledto a serial to parallel converter 360 configured to convert the serialsymbol stream to a plurality of parallel streams corresponding to thenumber of carriers in the OFDMA system.

The output of the serial to parallel converter 360 is coupled to a FastFourier Transform (FFT) module 362. The FFT module 362 is configured totransform the time domain symbols to the frequency domain counterpart.

The output of the FFT module 362 is coupled to a channel estimator 364that is configure to determine a channel and interference estimate basedin part on the forward link pilot signals. A carrier allocation module380, alternatively referred to as a resource allocation module, candetermine the sub-carriers assigned to the data and the sub-carriersassigned to the forward link pilot signals. The carrier allocationmodule 380 can determine the sub-carrier and segment assignments basedin part on any assignment messages received. The carrier allocationmodule 380 can, for example, implement a frequency hopping algorithm todetermine the current carrier assignment based on a past assignment. Thecarrier allocation module 380 is coupled to the channel estimator 364and informs the channel estimator 364 of the sub-carrier and segmentassignment.

The channel estimator 364 determines a channel and interference estimatebased on the forward link pilot signals. The channel estimator 364 canbe configured to estimate the channel and interference for each of thesegments of the OFDMA system. The channel estimator 364 can determine anestimate using a least squares method, a maximum likelihood estimate, acombination of least squares and maximum likelihood estimate, and thelike, or some other process of channel and interference estimation.

The output of the channel estimator 364 including the frequency domaintransform of the received symbols and the channel and interferenceestimates is coupled to a demodulator 370. The carrier allocation module380 can also inform the demodulator 370 of the sub-carrier frequenciesallocated to data transmission. The demodulator 370 is configured todemodulate the received data carriers based in part on the channel andinterference estimate. In some instances, the demodulator 370 may beunable to demodulate the received signals. As noted earlier, thedemodulator 370 may be unsuccessful because the channel quality isinadequate and cannot support the transmitted rate of the data, orbecause degradation attributable to inadequate channel and interferenceestimation is sufficiently severe to result in decoding error.

If the demodulator 370 is unsuccessful, it can generate an indication ofthe inability to demodulate the received signals. The demodulator 370can also provide an unsuccessful demodulation indication to thetransmitter module 354 in the transceiver 350 for transmission back tothe base station.

If the demodulator 370 is unsuccessful, the received data is dropped,and there is no need to couple any data to memory. If the demodulator370 is successful, the demodulator 370 can be configured to couple thedemodulated data to a parallel to serial converter 372 that isconfigured to convert the parallel demodulated data to a serial datastream. The output of the parallel to serial converter 372 is coupled toa data buffer 374 for further processing.

A channel quality indicator (CQI) module 390 can also be coupled to thechannel estimator 364 and can use the values of pilot power, channelestimate, and interference estimate to determine a value of the CQI foreach of the segments. In one embodiment, the CQI value is based in parton the SNR. The CQI module 390 couples the CQI value to the transmittermodule 354, which can be configured to transmit the value to the basestation using, for example, an overhead channel, control channel, ortraffic channel.

The wireless communication system can implement a channel characteristicreporting scheme that is configured to minimize the amount of reportingmessages that need to be communicated to the base stations. The wirelesscommunication system can implement channel reporting schemes thatrequire a user terminal to provide reporting messages on a periodicbasis, an assigned basis, a probabilistically determined basis, or someother basis or combination of bases.

If the wireless communication system implements a periodic reportingscheme, the period can correspond to a predetermined time. Thepredetermined time can be based on a symbol timing, and can be based ona frame of symbols or multiple frames of symbols.

The CQI module 390 can be configured to report the CQI or an index ofthe segment corresponding to the best frame, if the reporting periodspans multiple frames. In other embodiments, the CQI module 390 can beconfigured to average the CQI values over multiple frames and report theCQI or index of the segment having the best averaged CQI. In anotherembodiment, the CQI module 390 can be configured to report the CQI orindex of the segments exhibiting improving CQI values. The CQI module390 is not limited to any particular reporting criteria, and may usesome other criteria for determining which segment or segments to report,and the information included with the reporting message.

If the feedback channel capacity and link budget are not limited in asystem, each user terminal could transmit an array of CQI reportingmessages for all frequency segments. In such a brute force reportingscheme, each user terminal reports every CQI value corresponding toevery segment. However, this creates an enormous amount of unnecessaryinformation.

To improve the amount of overhead used for reporting CQI, the wirelesscommunication system can implement a reporting scheme where userterminals measure the forward link pilots and feedback the identity ofthe preferred frequency segment(s). In one embodiment, the userterminals determine a predetermined number of preferred segments and canreport the identity of the predetermined number of segments to thescheduler in one or more reporting messages. The predetermined numbercan be a fixed number or can be varied, for example, based on a controlmessage transmitted by the scheduler or a communication bandwidthdesired by the user terminal.

The user terminal can generate reporting messages that report a CQI foras few as one preferred segment or CQI values for as many as all of thesegments. In some embodiments, the number of segments identified in areporting message can depend on a bandwidth occupied or desired in thecommunication link to the user terminal. For example, a user terminalhaving a communication bandwidth that is less than a bandwidth of asegment may report as few as one segment CQI value or a segmentidentity. A second user terminal having a communication bandwidth thatis greater than the bandwidth of a single segment may report CQI valuesor segment identities for at least the number of segments needed tosupport the communication bandwidth.

In other embodiments, the wireless communication system may define morethan one local segment size, or multiple local segments can beaggregated to form a larger segment. In such an embodiment, the userterminal can report a desired preferred segment of any size, and thesegment size is not limited to a single segment size. In one embodiment,the user terminal can store a codebook with multiple segment sizes. Theuser terminal can determine a CQI value for each cluster or segment sizedefined in the codebook. The user terminal can report N of the bestsegment sizes based upon some predefined criteria, which may be part ofthe communication session or negotiated on a periodic basis.

The format of the reporting messages may be predetermined such that theuser terminal reports the identities of the one or more segments inorder of decreasing preference. Of course, other reporting messageformats may be used. For example, the user terminal may report a CQIvalue and corresponding segment identity for each reported segment thatis identified as a preferred segment.

The scheduler can use the reporting messages and other schedulingcriteria to determine the tones or sub-carriers that are assigned toeach of the user terminals. The wireless communication system can thususe the reporting messages to maintain communication links between basestations and user terminals over the segments that opportunisticallyprovide advantageous performance.

In an embodiment of a reporting scheme implementing an efficient channelpreference feedback algorithm, a user terminal can generate a reportingmessage using log₂L bits to indicate the segment with the best channelquality, where there are L segments in the system. The user terminaltransmits only the CQI of the best segment or only a segment indexcorresponding to the best segment in the feedback reporting message. Theuser terminal does not need to report L-1 CQI values corresponding tosegments with lesser CQI values.

The CQI module 390 can further reduce the feedback rate by implementingthresholding logic in best segment reporting. Given a long term averagechannel quality in SNR, the CQI module 390 can compare the SNRcorresponding to the best segment against the average SNR and choose notto report the CQI corresponding to the best segment unless it is apredetermined value, Δ, above the average. For example, the CQI module390 can generate the reporting message if the CQI corresponding to thebest segment is Δ dB above the average.

Thus, the CQI module 390 can have the opportunity to transmit areporting message on a periodic basis or on an assigned basis and mayselectively not transmit the reporting message based on the thresholdinglogic. For example, the CQI module 390 may be allowed to transmit areporting message in a predetermined time slot that occurs eachreporting interval, which can be, for example 15 ms. Alternatively, theCQI module 390 can be assigned a reporting time based on a round robinallocation of reporting slots to each of the user terminals in a basestation coverage area. The CQI module 390 can implement thresholdinglogic to further reduce the instances of reporting messages regardlessof the underlying reporting timing. In other embodiments, the CQI module390 can be configured to generate and transmit a reporting message whenthe thresholding logic is satisfied.

This thresholding mechanism can provide a manner for a scheduler tobalance the segment sensitive scheduling gain and reverse link feedbackcapacity. A scheduler in the wireless communication system can broadcastor multicast the desired threshold level, Δ, to user terminals based onreverse link feedback channel loading. High thresholds would lead toless reporting and low thresholds would lead to more reporting.

Alternatively, the scheduler can broadcast or multicast a desiredreporting rate directly. for example, the scheduler in the base stationcan transmit a desired percentage of time a user terminal is allowed toreport the best segment. Each CQI module 390 in a user terminal cantranslate the desired reporting rate into a Δ dB threshold based onhistorical channel characteristic statistics maintained by the userterminal. For example, the CQI module 390 can collect the CQI valuesdetermines for each of the segments and can generate a distribution ofthe CQI values over time. The CQI module 390 can, for example, generatea Cumulative Distribution Function (CDF) based on the historical values.The CQI module 390 can then determine a threshold based on the desiredreporting percentage and the CDF. For example, a reporting rate of 0.3can corresponds to a 70% CDF quantile and Δ=5 dB reporting threshold.The CDF maintained by each CQI module 390 can be distinct, because theyare established based on the channel characteristics experienced by theuser terminal. Furthermore, the CDF may change over time, as the channelcharacteristics experienced by the user terminal change, for example,due to mobility or changes in the multipaths in the environment.

If HARQ is deployed in a system, the CQI module 390 can be configured toinclude the average CQI across all frequency segment the feedbackreporting message. Although the conservative CQI will lead to thescheduling of low spectral efficiency transmission, early termination ofHARQ is likely to retain a substantial fraction of the achievablecapacity gain given reasonable HARQ granularity. This approach alsoimprove the robustness of segment sensitive scheduling in the cases whenthe scheduled segment is not the best one and may possibly be a poorselection, because of, for example, channel decorrelation betweenchannel measurement time and the actual transmission time, measurementmismatch, or some other factors.

FIG. 4 is a simplified flowchart of an embodiment of a method 400 ofsegment sensitive scheduling. The method 400 can be performed, forexample, by the scheduler in an OFDMA wireless communication system,such as a scheduler in a base station shown in the system of FIG. 1. Forexample, the scheduler shown in the base station transmitter of FIG. 2can be configured to perform the method 400. The scheduler can performthe method 400 for each of the users. For example, the scheduler canperform the method for each of the forward link and reverse linksestablished between a base station and user terminals in the basestation coverage area.

The method 400 begins at block 402 where the scheduler partitions theoperating band into a plurality of segments. The wireless communicationsystem can define the segments, and the segments can include one or moreglobal segments and one or more local segments. The global segments caninclude a subset of the sub-carriers of the OFDMA system that spansubstantially a large fraction of the operating band. The globalsegments typically are assigned non-contiguous frequency spanscomprising one or more sub-carriers. The local segments can becontiguous or non-contiguous bands that include one or moresub-carriers. The local segments typically have a bandwidth that is lessthan a coherent bandwidth of the wireless channel. In some cases thesegments may be pre-partitioned in a predetermined manner and known toboth the base station and mobile station. As such, this functionalitymay be omitted.

The scheduler need not perform any actual physical partitioning of theoperating band, but may instead, merely account for the various segmentsand the sub-carriers associated with each segment. The schedulertypically associates each sub-carrier with only one segment, and eachsegment includes a distinct subset of sub-carriers.

The scheduler proceeds to block 410 and determines user dataconstraints. Such user data constraints can include data latencyconstraints, bandwidth constraints, and other constraints that may beassociated with particular users or communication links. The schedulercan be configured to attempt to satisfy substantially all dataconstraints when scheduling the segment.

After receiving the data constraints, the scheduler proceeds to decisionblock 420 to determine if the channel for a particular user requireshigh bandwidth. In the context of the scheduler, the term high bandwidthrefers to a user that requires a resource assignment that exceeds thebandwidth of a predetermined number of local segments. The predeterminednumber of local segments can be, for example, one, or can be some othernumber greater than one. High data rate users can require transmissionof signals over a large fraction of the total bandwidth, which reducesthe potential gain of scheduled transmission over average channel SNR.

If the user requires high bandwidth, the scheduler proceeds to block 430and assigns the user to a global segment and assigns sub-carriers fromthe assigned global segment. The scheduler then proceeds from block 430back to block 410.

If, at decision block 420 the scheduler determines that the user doesnot require high bandwidth, the scheduler proceeds to block 440 anddetermines a segment preference for the user and communication link. Thescheduler can determine a segment preference based on channel analysis,channel characteristic reporting messages; or a combination of analysisand reporting messages.

In one embodiment, the scheduler can determine a channel estimate foreach local segment in the operating band based on a pilot signaltransmitted by the user terminal. The scheduler can compare all of thechannel estimates to determine the segment preference as the segmentthat has the best channel characteristics. For example, the schedulercan determine, based in part on the channel estimates, which of thesegments has the highest SNR.

In another embodiment, the scheduler can receive reporting messages fromsome or all of the user terminals. The reporting messages can include asegment preference or can include channel characteristics that thescheduler can use to determine a segment preference.

After determining the segment preference for a particular user, thescheduler proceeds to decision block 450 to determine whether thesegment preference differs from a previous segment preference for thatsame user.

If the scheduler determines that the segment preference has changed, thescheduler proceeds to block 460 and assigns a segment and sub-carriersfrom the segment to the communication link. In the forward linkdirection, the scheduler can assign a channel by controlling a signalmapper to map the data signal for the user terminal to the appropriatesub-carriers in the preferred segment. In the reverse link direction,the scheduler can generate a segment assignment message that identifiesthe segment and sub-carriers assigned to that user terminal. Aftersegment assignment, the scheduler proceeds back to block 410.

The wireless communication system can implement sticky or persistentassignments. The user terminal can use the same assignment until itreceives a de-assignment message. In one embodiment, the de-assignmentmessage can be an assignment message to a distinct user terminal for asub-carrier for which the user terminal is assigned.

If, at decision block 450, the scheduler determines that the segmentpreference has not changed, the scheduler proceeds to block 470. Atblock 470, the scheduler can provide some form of interference diversityby implementing frequency hopping. The scheduler can be configured toenforce frequency hopping within the assigned segment in order tomaintain the advantages of segment sensitive scheduling. After enforcingthe frequency hopping on the assigned sub-carriers, the schedulerproceeds back to block 410.

FIG. 5 is a simplified flowchart of an embodiment of a method 500 ofchannel characteristic reporting in a system implementing segmentsensitive scheduling. As noted above, the scheduler can utilizereporting messages as part of the segment sensitive scheduling process.The manner in which reporting messages are generated and transmitted tothe scheduler can affect the amount of overhead required to supportreporting messages. The reporting method 500 can be performed, forexample, by a user terminal of the wireless communication system of FIG.1 to assist in scheduling of forward link OFDMA channels.

The method 500 begins at block 510 where the user terminal receives theforward link pilot signals. The user terminal proceeds to block 520 anddetermines channel characteristics for each of the predetermined localsegments in the operating band. The user terminal can, for example,determine the signal level, interference level, SNR over the segment, orsome other channel characteristic for each local segment. The userterminal can also determine channel characteristics, such as an averagechannel strength or average SNR for each of the global segments.

The user terminal proceeds to block 530 and determines a preferredsegment from the various segments. A high bandwidth user may prefer aglobal segment to any local segment merely due to the ability of theglobal segment to satisfy the bandwidth requirements. If there aremultiple global segments, the user terminal can determine a globalsegment having the greatest average SNR as the preferred segment.

Alternatively, fit the user terminal is assigned to a local segment orcapable of assignment to a local segment, the user terminal determineswhich of the segments is the preferred segment. The user terminal can,for example, select the local segment that corresponds to the highestSNR or channel power. In another embodiment, the user terminal mayselect the segment having the least interference. In another embodiment,the user terminal can select a preferred segment based on a variety offactors.

After determining the segment preference, the user terminal proceeds todecision block 540 to determine whether a reporting constraint issatisfied. The user terminal can include a number of reportingconstraints and may generate and transmit a reporting message only whena predetermined number of constraints are satisfied. The user terminalcan limit the reporting messages using the reporting constraints inorder to minimize the amount of reporting overhead communicated to thescheduler.

For example, the user terminal can limit reporting to messages thatreport SNR values greater than a predetermined threshold above anaverage channel SNR. The predetermined threshold can be static or can becommunicated from the scheduler. Additionally, the user terminal can belimited to only reporting segment preferences that are distinct from thesegment in which the user terminal is presently operating.

If the user terminal does not satisfy the reporting constraints, theuser terminal returns to block 510 and does not generate a reportingmessage. Alternatively, if at decision block 540 the user terminaldetermines that the reporting constraints have been satisfied, the userterminal proceeds to block 550 and generates a reporting message.

The user terminal can, for example, generate a reporting message thatidentifies the preferred segment or a plurality of preferred segments.The user terminal can, for example, report an index corresponding to thepreferred segment. The user terminal may also include in the reportingmessage other channel characteristics, such as an average CQI over allsegments.

After generating the reporting message, the user terminal proceeds toblock 560 and transmits the reporting message to the scheduler. Forexample, the user terminal can transmit the reporting message ormessages to a base station on a reverse link overhead channel. The userterminal returns to block 510 to repeat the channel analysis andreporting method 500.

Methods and apparatus for segment sensitive scheduling have beendescribed. An OFDMA wireless communication system can implement segmentsensitive scheduling to improve the performance of the communicationlinks. The wireless system can partition the operating band into anumber of segments, including global segments and local segments. Ascheduler in the system can be configured to assign a segment andsub-carriers within the segment to each communication link based onchannel characteristics. The channel characteristics can be determinedat the scheduler using channel analysis or can be determined at thereceiver and fed back to the scheduler in one or more reportingmessages.

Reporting constraints can be imposed on the reporting messages to limitthe overhead needed to support the reporting messages. The reportingconstraints can limit the amount of information reported and can limitthe instances of reporting messages. For example, the reporting messagescan be limited to reporting a CQI value or segment index for a segmentpreference. The reporting messages can be limited to reporting on apredetermined periodic basis or an assigned basis such as in round robinreporting where each user terminal in a base station coverage areareports one time before any user terminal transmits an updated reportingmessage. The reporting messages can also be limited to a probabilisticbasis, where reporting is limited based on a probability that the userterminal will experience a preferred segment that is substantiallybetter than an average channel characteristic.

The wireless communication system can improve the overall systemperformance by utilizing segment sensitive scheduling.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), a Reduced Instruction Set Computer (RISC) processor, anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. A generalpurpose processor may be a microprocessor, but in the alternative, theprocessor may be any processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, for example, a combination of a DSP and amicroprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method, process, or algorithm described in connectionwith the embodiments disclosed herein may be embodied directly inhardware, in a software module executed by a processor, or in acombination of the two.

A software module may reside in RAM memory, flash memory, non-volatilememory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, aremovable disk, a CD-ROM, or any other form of storage medium known inthe art. An exemplary storage medium is coupled to the processor suchthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. Further, the various methods may be performed in theorder shown in the embodiments or may be performed using a modifiedorder of steps. Additionally, one or more process or method steps may beomitted or one or more process or method steps may be added to themethods and processes. An additional step, block, or action may be addedin the beginning, end, or intervening existing elements of the methodsand processes.

The above description of the disclosed embodiments is provided to enableany person of ordinary skill in the art to make or use the disclosure.Various modifications to these embodiments will be readily apparent tothose of ordinary skill in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the disclosure. Thus, the disclosure is not intendedto be limited to the embodiments shown herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

1. An apparatus for channel sensitive scheduling in a communication system including a plurality of sub-carriers spanning an operating frequency band, the apparatus comprising: a receiver module configured to receive a reverse link pilot signal and at least one channel characteristic reporting message; and a scheduler coupled to the receiver module and configured to determine, based on the reverse link pilot signal, a channel characteristic corresponding to each of a plurality of segments spanning the operating frequency band, each of the segments having a bandwidth less than a total bandwidth, the scheduler configured to determine a reverse link resource assignment based on the channel characteristics and further configured to determine a forward link resource assignment based on the at least one channel characteristic reporting message.
 2. The apparatus of claim 1, wherein the channel characteristic comprises a signal to noise ratio (SNR) value.
 3. The apparatus of claim 1, wherein the channel characteristic comprises an interference value.
 4. The apparatus of claim 1, further comprising a signal mapper coupled to the scheduler and configured to map data symbols to forward link sub-carriers in accordance with the forward link resource assignment.
 5. The apparatus of claim 1, wherein the scheduler is configured to assign sub-carriers corresponding to a global segment comprising a non-contiguous subset of the plurality of sub-carriers that span a substantial fraction of the operating frequency band for channels requiring a bandwidth greater than the coherent channel bandwidth.
 6. An apparatus for channel sensitive scheduling in a communication system including a plurality of sub-carriers spanning an operating frequency band, the apparatus comprising: means for determining a channel preference indicative of a preferred segment from a plurality of segments substantially spanning at least a portion of the operating band based upon channel characteristics experienced by a receiver; and means for assigning a subset of sub-carriers within the preferred segment to a particular communication link associated with the channel preference.
 7. The apparatus of claim 6, wherein the means for determining the channel preference comprises: means for receiving a pilot signal; means for determining a channel characteristic corresponding to each of the plurality of segments; and means for selecting the channel preference based on the channel characteristics.
 8. The apparatus of claim 6, wherein the means for determining the channel preference comprises means for receiving a channel reporting message indicative of the channel preference.
 9. A method of reporting channel characteristics in a communication system including a plurality of sub-carriers spanning an operating frequency band, the method comprising: receiving a pilot signal; determining a channel characteristic corresponding to each of a plurality of segments spanning the operating band, each segment having a bandwidth less than a coherent channel bandwidth; determining a preferred segment from the plurality of segments; comparing the channel characteristic corresponding to the preferred segment to a reporting threshold; and generating a reporting message based on the preferred segment if the channel characteristic corresponding to the preferred segment exceeds the reporting threshold.
 10. The method of claim 9, further comprising transmitting the reporting message to a scheduler.
 11. The method of claim 9, wherein the pilot signal comprises a forward link pilot signal.
 12. The method of claim 9, wherein the channel characteristic comprises a signal to noise ratio (SNR).
 13. The method of claim 9, wherein the channel characteristic comprises an interference value.
 14. The method of claim 9, wherein the channel characteristic comprises a pilot signal strength.
 15. The method of claim 9, wherein determining the preferred segment comprises selecting a segment corresponding to a largest signal to noise ratio.
 16. The method of claim 9, wherein determining the preferred segment comprises selecting a segment corresponding to a least interference value.
 17. The method of claim 9, wherein comparing the channel characteristic corresponding to the preferred segment to the reporting threshold comprises determining whether a signal to noise ratio corresponding to the preferred segment exceeds an average SNR ratio by a predetermined amount.
 18. The method of claim 9, wherein comparing the channel characteristic corresponding to the preferred segment to the reporting threshold comprises: receiving a differential value from a scheduler; and determining whether a signal to noise ratio corresponding to the preferred segment exceeds an average SNR ratio by the differential value. 